1. Field of the Invention
The invention relates to a driven axle assembly with a lubricant circulation system, wherein the axle assembly comprises:
an axle housing with a main drive and a lubricant liquid in its inside, PA1 hollow axle casings fixed to both sides of the axle housing, PA1 a hollow wheel hub rotatably connected to each axle housing, the wheel hub having a flange for carrying a vehicle wheel rim as well as, in its inside, a planetary gearing and, preferably, a multi-plate friction type wet brake, the main drive and the planetary gearing as well as the multi-plate wet brake being interconnected with a drive shaft on both sides of the main drive, respectively, and PA1 means for making a lubricant liquid flow within the axle assembly. PA1 an axle housing with a main drive and a lubricant liquid in its inside, PA1 hollow axle casings fixed to both sides of the axle housing, PA1 a hollow wheel hub rotatably connected to each axle housing, the wheel hub having a flange for carrying a vehicle wheel rim as well as, in its inside, a planetary gearing and a multi-plate friction type wet brake, the main drive and the planetary gearing as well as the multi-plate wet brake being interconnected with a drive shaft on both sides of the main drive, respectively, and PA1 means for making a lubricant liquid flow within the axle assembly.
2. Description of the Related Art
In driven axle assemblies of heavy duty vehicles such as muckshifters, mining machines, agricultural power machines and vehicles for handling and transporting materials, there are to basic tasks to be solved by the applied lubricant circulation system: first, to provide sufficient lubrication under all operational conditions and, second, to avoid overheating of the constructional parts within the axle assembly.
The driven axle assemblies of vehicles as mentioned above, however, comprise more than one drive gear unit with quite complicated and sophisticated gearing mechanisms as well as multi-plate brake units. In the rule, two side drives are arranged on both sides of a main drive within one axle assembly all of them having one and the same oil filling. From out of this one oil filling, all lubrication and cooling problems must be solved in an axle assembly. From among these difficulties, the cooling requires the more intensive lubricant circulation since breaking action produces a considerable heat amount in the plates of the multi-plate friction type wet brake.
During and after the braking action, the temperature of the thin oil film between the brake plates will be arisen until or over the deterioration temperature limit of the oil. Namely, the high temperature of the oil triggers the distillation procedure of the oil and the bitumen which is one of the side product of this distillation, gets deposited on the surface of the brake plates quite quickly. The organic friction layer on the brake plates gets saturated with bitumen, and these result in the drastical decrease of the friction coefficient between the brake plates. In the end effect, the vehicle cannot be further operated because of the total lack of brake function.
The increased heat within the multi-plate friction type wet brake causes the organic friction layer to get loosened from the steel base plate and/or it gets burned. The removed particles of the friction layer pollutes the lubricant, deteriorate the lubrication effect, cause sediments on gears and bearings.
In case of known axle assemblies (as it is described inter alia in GE patent specification No. 36 38 862), the centrifugal effect of the driving motion of the brake plate is used to make the oil circulation more effective. This solution, however, is suitable to circulate the oil only within the wheel hub and, thus, the amount of oil to be used for cooling is very limited. Therefore, this kind of prior art solutions is able to deflect only a relatively small amount of heat and is not suitable to conduct the heat away, out of the wheel hub. In the practice, this solution is not secure enough since the produced heat amount is often greater than the dissipated one, especially under unfavourable operation conditions of the vehicle. Just under these conditions, it is eminent to have reliable breaking effect.
To provide a reliable heat balance of produced and dissipated heat, it has been proposed (in e.g. GE patent specification No. 23 63 104) to separate the oil chamber of the multi-plate friction type wet brake from the oil chamber of the wheel hub and to provide a separate cooling for the brake plates arranged in a closed chamber from outside. Therein, a separate cooling system operated with water is provided for cooling the brake plates. It is needles to say that this arrangement is very complicated and its operation is troublesome: one has to control the water cooling system tightly separated from the oil circulation system.